Messages in this thread | | | Date | Fri, 3 Oct 2014 16:23:28 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v6 2/6] arm64: ptrace: allow tracer to skip a system call |
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On Wed, Oct 01, 2014 at 12:08:05PM +0100, AKASHI Takahiro wrote: > Will, > > When I was looking into syscall_trace_exit() more closely, I found > another (big) problem. > There are two system calls, execve() and rt_sigreturn(), which change > 'syscallno' in pt_regs to -1 in start_thread() and restore_sigframe(), > respectively. > > Since syscallno is not valid anymore in syscall_trace_exit() for these > system calls, we cannot create a correct syscall exit record for tracepoint > in trace_sys_exit() (=> ftrace_syscall_exit()) and for audit in audit_syscall_exit(). > > This does not happen on arm because syscall numbers are kept in > thread_info on arm. > > How can we deal with this issue?
How is this handled on other architectures? x86, for example, seems to zero orig_ax when restoring the sigcontext, but leaves it alone in start_thread.
What is the impact of this problem? AFAICT, we just miss some exits, right (as opposed to an OOPs or the like)?
Will
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